The single most dangerous ball for a right-handed batsman is the 90 mph
delivery from a left-arm bowler that swings late on the line of the stumps.

His pads are no longer the batsman's second line of defence: if he gets them in the way of the ball, he is gone, lbw. And if the bowler is tall, and has already banged in a couple of bouncers, the batsman will be all the more reluctant to push forward in hope.

England do not have such a Test bowler, and never really have had. Australia do: Mitchell Starc, who is one fine cricketer in the making, as he is also a dangerous late-order batsman.

The worst-case scenario for England in this series is for Australia to win the toss on a damp morning at Trent Bridge and for Starc to have one of his magic spells when he makes the ball boomerang at 90 mph.

England are rolled over cheaply - as they usually are in the first Test of an Ashes series - then the sun comes out and Australia, buoyantly revived, are launched by Shane Watson. England are dismissed a second time by scoreboard pressure and Australia go to Lord's, their favourite venue through the ages, 1-0 up.

Starc has already had one of his magic spells on this tour. Fortunately for Somerset, he did it with the second new ball at Taunton, not the first, but the effect was still paralysing.

He took four wickets for no runs as Somerset went from 304-2 to 320 all out. Two batsmen bowled, including Craig Kieswetter, and two lbw. Yes, 4-0. In this period of scientific preparation, bowlers don't do that sort of thing - unless they are left-arm fast and can swing it.

And for an Ashes series in England, this is a new form of warhead. Australia have had a couple of fine left-armers before, but Alan Davidson, who led Australia's attack in 1961, was not so quick and tall - Starc is 6' 5" - and Bruce Reid never toured England because he was so injury-prone, although he gave England hell in 1990-91.

At least England have had the benefit of some recent practice. By playing interminably against New Zealand for the first half of this calendar year, England's batsmen saw a lot of Trent Boult and Neil Wagner. Neither was so tall or quick as Starc, but Boult still recorded a career-best 'six-for' in the second Test at Headingley.

Boult, more than Wagner, also gave England an advantage as well as trouble. In his follow-through, when bowling over the wicket, Boult created rough areas into which Graeme Swann aimed his off-breaks in New Zealand's second innings. Swann finished with 10 wickets; without those footmarks England probably would not have had time to force a win.

Starc, however, is already - at 23 - an accomplished performer in bowling round the wicket. He has picked the brains of Wasim Akram, so that when the ball is old he switches from over to round and reverse-swings it away from the right-hander. Not quite so lethal but still…

Indeed, Starc has a wise head on his shoulders. He could have gone to the Indian Premier League for a hefty fee but preferred to play for Yorkshire last season, getting to know English grounds, balls and conditions ahead of this summer, and picking the brains of their left-arm pace bowler Ryan Sidebottom.

It is a shame for England that they do not have a counterpart to Starc to call on and that all their bowlers are right-arm. This lack of diversity has been another of the reasons why England were unable to cling on to No 1 in the world Test rankings.

Or do they? On Sunday and Monday at Chelmsford, England were ruffled and roughed up by Essex's 20 year-old Tymal Mills. Mills was being laughably labelled as 'IMF' (left-arm medium-fast) by cricket's premier website while he was in the process of clocking 94 mph, hitting Tim Bresnan on the head and Swann on the right-arm, and coming within a whisker of sabotaging England's Ashes campaign.

Mills also had Alastair Cook caught behind after pitching in his corridor of uncertainty - most pace bowlers have wasted their breath bowling across Cook - which showed the Australians exactly what line Starc should bowl to England's captain on July 10.

It is probably expecting too much of Mills to perform this summer for England as he doesn't yet swing the new ball into right-handers as much as Starc. But, if taken to Australia this winter, Mills might avenge England's defeat at Perth on their last tour, when Mitchell Johnson had one of his magic spells.

In the meantime, England have to contend with Starc the bowler and late-order batsman. In the Mohali Test earlier this year, he scored an attacking 99 off 144 balls and a defensive 35 to prove he is a proper left-handed batsman, not just a hitter.

Against South Africa, in a Test at Perth shortly before, he belted an unbeaten 68 off 43 balls at No 10 - shortly after taking a 'six-for'. And these forthright forays were conducted without anybody at the other end to guide him, in other words before Brad Haddin was recalled to marshal Australia's lower order from No 7.

The only question about Starc is whether he is too nice to be a fast bowler: is there enough animal or mongrel in him? He runs in with a beautiful smoothness - his younger brother Brandon is no less athletic and represents Australia as a high-jumper - and so far he has succeeded at cricket without turning ugly.

Over the next six months one of the most fascinating themes will be to see how Australia's fast left-armer develops - and how England cope with the Starc reality.